As shown in FIG. 1, a linear drive apparatus 15 in the prior art is concretely applied in a solar-energy tracker, and mainly used for tracking and driving an elevation angle (also an azimuthal angle) of a solar-energy biaxial tracker and for driving a uniaxial tracker. The linear drive apparatus in the prior art mainly has the following problems:
1. When the solar tracker (biaxial and uniaxial) is designed, the center of gravity of a moving part shall coincide with (closely) a rotation axis, thereby decreasing the drive torque needed during tracking to further meet the requirement of low energy consumption of the tracker itself. In practical engineering applications, due to the special structural constraints of the tracker, such a driver, in addition to providing driving force, also provides the support and the stabilizing effects for the moving part. Under the influence of big wind and heavy snow, the requirement for the stiffness (resistance to deflection) of the driver is very high, that is to say, such a driver shall provide sufficient driving force while having high anti-load capacity and adequate stiffness (resistance to deflection), thus guaranteeing that the tracker can accurately track and stably operate.
Such a driver in the prior art for the solar tracker and the desired driving force are taken as design basis. The length-diameter ratio of such a drive screw is designed to be 30-40, and the length-diameter ratio of a drive nut is designed to be 1.5-2. A deep groove ball bearing is used for the rotation part of the screw, which can meet the requirement of the driving force but in which the rigidity and anti-load capacity of the driver are limited. Furthermore, an extension rod of the driver in the prior art is in a big-gap fit with an outer tube. In engineering applications, when the driver is pulled and pressed by the rotation part of the tracker, the gap increases the deflection of the screw and facilitates the tracker shake not to track precisely.
2. In practical applications of the solar tracker, the tracker is operated under a variety of extreme conditions outdoors all the year round. As a key component of the tracker, such a driver must have very high degree of protection, and must ensure that a lubrication system runs well all lifetime.
The extension rod of the driver in the prior art is in the big-gap fit with the outer tube. In practical application, water, dust and debris are easily entered into the inner part of the driver, thus influencing a drive system (a gear and a screw drive nut) of the driver (even electrical systems), and seriously affecting the normal operation of the tracker. Even if some apparatuses are provided with a dustproof cover, due to the working environment of the apparatus itself, the dustproof cover is very easily aged and damaged. Once damaged, it will also face these problems.
3. In the practical applications of the solar tracker, the signal feedback of the driver is a key for the tracker to accurately track. An accurate and reliable signal feedback system is a necessary condition for the normal operation of the tracker.
A common gear transmission is adopted to drive such a driver motor and the screw. The integral signal feedback system of the gear transmission is in non-sealing process with an interface of the screw. In practical applications, the rainwater infiltrated through the extension rod can directly reach the inner part of the transmission, causing the gear to be rusted, and the signal feedback system to have short-circuit. It produces ice under a low temperature environment, thus causing the driver not to work. Furthermore, the signal feedback system of the driver is designed to be integrated with the transmission, thus increasing the difficulty of maintenance and replacement.
4. Such a driver in the prior art adopts the current monitoring of the motor to achieve protection. A complicate external circuitry is needed to be provided and a system hardware is needed to comprise an A/D conversion module, taking up a lot of system resources. As to the current monitoring of the motor in the prior art, the voltage change on resistance is sampled through the influence caused after the current change of the resistance is sampled externally. A control system, through judging the voltage of sampling resistance, monitors the current of the motor. The method also has the disadvantages of larger errors and no timely reaction.